Abstract
In order to make it clear for the strain effects of lanthanum-based 214 phase superconducting thin films, we prepared three kinds of thin films : (1) La2-xSrxCuO4 ( x=0.1~0.15 ) deposited on LaSrAlO4(001) substrates, (2) La2-xSrxCuO4 ( x=0.075~0.15 ) deposited on LaSrAlO4(100) substrates, (3) La2-xMxCuO4 ( M=Ba,Sr,Ca,Mg ; x=0.1 ) deposited on LaSrAlO4(001) substrates. Compared the results of films deposited on (001) and (100) orientation substrates, we found that two opposite substrate-induced epitaxial strains had a similar evolution of physical properties, which are enhanced Tc and linear normal-state R-T curve. Therefore, we speculated that only c-axis expansion was not the major factor altering physical properties so drastically. The excess oxygen intercalation may play an important role as well. On the other hand, the substitution of alkaline-earth element induced intrinsic strain in thin films, it may adjust the space of interstitial sites between two La-O layers occupied by excess oxygen, and thus changed the oxygen content in the film substituted for different alkaline-earth elements (oxygen content: Ba2+ □ Sr2+ > Ca2+ > Mg2+ ). This is another evidence that the excess oxygen is important in the physical properties of lanthanum-based 214 phase superconducting thin films.